1. Field of the Invention
The present invention relates generally to the field of scintillation camera and image display forming apparatus and more particularly to a method and apparatus for correcting for the spatial distortion of scintillation cameras.
2. Description of the Prior Art
Distortion in the image or image data obtained from scintillation cameras and associated image display apparatus is primarily due to variations in point source sensitivity and spatial distortion. In presently available scintillation cameras known as the "Anger-type", variations in point source sensitivity are maintainable in well designed camera systems with proper tuning and adjustment to within 1-2%. Spatial distortions are the result of systematic errors in the positioning of scintillation events largely due to non-linear changes in the light distribution in the scintillation apparatus as a function of location; i.e. events are not recorded in their correct locations with respect to the overall image. The result is localized image event compression or expansion appearing in the image as erroneous variations in image intensity. Thus, even though the displacements of individual events are not visually apparent in the image, spatial distortions cause noticeable field intensity non-uniformities.
The prior art utilizes various techniques to attempt to correct for the spatial distortions and field non-uniformities in scintillation cameras.
One distortion correction method of the prior art utilizes image processing to appropriately increase or decrease the total counts or image events in a particular area by using information from previously acquired field floods. However, these methods do not correctly compensate for the primary causes of non-uniformities, namely spatial distortion.
Another method of the prior art disclosed in U.S. Pat. No. 3,745,345 which issued to G. Muehllehner on July 10, 1973 measures the spatial distortion of an Anger camera to obtain coordinate corrections factors for the camera. The coordinate corrections factors are stored in the camera and image forming apparatus for use in correcting an image. The correction factors are stored on an elemental image area basis with each elemental image area having a predetermined area. An uncorrected digital image or map is accumulated in an analyzer. A data system, in one arrangement, takes the image event count information on an elemental area basis and redistributes the accumulated counts in each elemental area into new image area locations in accordance with the coordinate corrections factors. In another arrangement, the coordinate correction factors are utilized to correct the signals corresponding to each scintillation event. The coordinate corrections factors are obtained from image data taken from a regular array of point sources at known image point locations. An apertured plate provides the array of point sources and multiple exposures are performed with the plate being shifted to a different predetermined orientation for each exposure.
Other distortion correction and distortion measurement techniques include the analysis of image data obtained from line patterns, scanning a point source across the image field, and full image area field floods. In the full field flood techniques, the gradient of the field flood is utilized to indicate correctional shifts.
While the above described prior art arrangements are generally suitable for their intended purpose, it would be desirable to provide a method and apparatus for improved correction of spatial distortion characteristics of Anger scintillation cameras and the like.